This invention relates to rotary crushers for pulverizing solid materials, and to a method and system for classifying the pulverized product. In particular, it relates to a rotary crusher having the capability with very little adjustment to provide relatively uniform product particle sizes ranging from rather large chunks to very fine powders. The invention also features a collection system for finely ground material which permits the crusher exhaust to assist in the recovery and classification of finely ground material.
Commercial crushers are required to perform a wide variety of crushing chores. For example, it may be desired to reduce the size of ordinary rock from 6"+ to -3/4" for use as paving aggregate. Alternatively, to prepare mineral-containing ore for chemical processing it may be desired to crush chunks of ore to a product size of approximately 30 mesh. In other instances, such as the pulverizing of coal for use in utility boilers, or cement manufacture, product particle sizes of 100 to 200 mesh may be required. At the present time, no single available crusher can satisfy the wide variety of product distributions and product sizes which may be desired without extensive modification. Accordingly, there is a substantial demand for a crusher which is sufficiently flexible to provide utility for a large number of feed materials and product size and distribution.
Rotary crushers of the general type disclosed herein have been described in my existing U.S. Pat. Nos. 3,887,141; 4,037,796; and 4,077,574. These patents disclose a crusher having an impact rotor positioned within a reduction chamber and having a plurality of hammerheads around its periphery. Ore entering the reduction chamber is directed tangentially against the hammers and hurled against the sides of the reduction chamber. The internal walls of the reduction chamber are lined with shatterbars which assist in reduction of the ore to a finer particle size. As particles fall to the bottom of the chamber, they are swept back into the downstream side of the reduction chamber by a rapidly moving fluidizing rotor located beneath the impact rotor. Air enters the reduction chamber through inlets in its side, and crushed particles are swept upwardly through a vertical classification chamber to permit removal of particles within certain size ranges. As shown in U.S. Pat. No. 4,037,796, particle diverter plates and air deflector flaps are used within the classification chambers to direct particles of various sizes into their proper classification.
With the prior art devices, particle size distribution is relatively fixed by the crusher design. While some flexibility exists to produce a very finely pulverized product by adjusting rotor speed, air flow, and classification chamber height, these mills can handle only a relatively narrow variety of feeds and product size distribution requirements. It has been found that with relatively minor modifications, the crusher described in U.S. Pat. No. 4,037,796 can be designed to do the work of three separate crushers; i.e., having product particle sizes corresponding to ranges generally referred to as secondary, tertiary, and fine grinding. In addition, it has been discovered that energy generated by the rotating hammers can be used to classify finely ground materials into a plurality of desired product distributions.
The crusher and classification system of the invention are characterized by the crusher having three separate and independent product takeoff points, including 2 exits used for very light crushing operations (i.e., where the product particle size is relatively large). In addition, the crusher is characterized by an offset unimpeded vertical attrition chamber, containing no deflectors or product removal means, where the attrition of rising small particles with falling larger particles creates further particle comminution. In addition, product classification from the exhaust from the crusher is effected through the use of the energy contained in the air/particle stream to assist in classifying the product. This classification may be accomplished by thrusting the product stream into a centrifugal separator, such as a cyclone collector, wherein the larger particles exit the bottom of the unit and smaller particles are carried across the top thereof. Alternatively, the product exit stream may be directed horizontally across a series of bins, with the larger particles falling by gravity into the bins nearest the exit, and smaller particle sizes falling at a greater distance from the exit.